1. Field of the Invention
The present invention is directed to waveguides, and more particularly, to waveguide structures incorporating a plurality of laterally extending segments.
2. Description of the Related Art
Low loss single-mode waveguides in thin Silicon-On-Insulator (SOI) have been demonstrated. Such waveguides may comprise, for example, a patterned silicon pathway formed on a silicon dioxide layer that is formed over a substrate. Light is substantially guided within the patterned silicon pathway.
Advantageously, these waveguides can be substantially thin. The thin geometry is helpful in obtaining high field concentrations in the waveguide cladding. Intense field concentrations in the cladding may be useful, for example, in the construction of sensors where interactions of the cladding with external stimulus perturb the propagation of light in the waveguide. The stimulus can thereby be sense by monitoring the optical output of the waveguide.
One of the outstanding problems of this geometry, however, is the difficulty of establishing an electrical contact with the waveguide without causing large losses in the optical mode. This problem is particularly troublesome when a DC or RF electrical field is to be applied directly to the waveguiding region. Such an applied electrical field can be used, for instance, to induce modulation through an electrically controllable index shift in the cladding; see e.g., B. Maune, R. Lawson, C. Gunn, A. Scherer, L. Dalton, “Electrically tunable ring resonators incorporating nematic liquid crystals as cladding layers,” Applied Physics Letters 83, 4689-4691 (2003). To provide single mode propagation, the waveguides are particularly small. In general, a tradeoff exists between establishing good electrical contact, which often requires the use of a metal or a highly doped semiconductor region in close proximity to the optical mode, and providing a low-loss waveguide. If, for instance, a metal contact is placed directly onto a high-index-contrast silicon-on-insulator waveguide, with a mode that is less than 1 micron FWHM, the optical losses associated with that metal will be substantially large. The challenge is electrically contacting a compact, high index contrast optical waveguide without inducing large optical losses.